The present invention relates generally to internal drum scanner assemblies and laser imaging systems incorporating such scanner assemblies. In particular, the present invention relates to a mechanism for aligning and centering film into a scanning position in an internal drum type scanner assembly, suitable for use in a medical imaging system.
Laser imaging systems are commonly used to produce photographic images from digital image data generated by magnetic resonance (MR), computed tomography (CT) or other types of scanners. Systems of this type typically include a continuous tone laser imager for exposing the image on photosensitive film, a film processor for developing the film, and an image management subsystem for coordinating the operation of the laser imager and the film processor.
The digital image data is a sequence of digital image values representative of the scanned image. Image processing electronics within the image management subsystem processes the image data values to generate a sequence of digital laser drive values (i.e., exposure values), which are input to a laser scanner. The laser scanner is responsive to the digital laser drive values for scanning across the photosensitive film in a raster pattern for exposing the image on the film.
The continuous-tone images used in the medical imaging field have very stringent image-quality requirements. A laser imager printing onto transparency film exposes an image in a raster format, the line spacing of which must be controlled to better than one micrometer. In addition, the image must be uniformly exposed such that the observer cannot notice any artifacts. In the case of medical imaging, the observers are professional image analysts (e.g., radiologists).
Film exposure systems are used to provide exposure of the image on photosensitive film. Known film exposure systems include a linear translation system and a laser or optical scanning system. The laser scanning system includes a laser scanner with unique optical configurations (i.e., lenses and mirrors), for exposure of the image onto the film. A linear translation system is a mechanical device that converts rotary motion into linear motion. The linear translation system provides for movement of the laser scanning system in a direction perpendicular to the scanning direction, such that a full image may be scanned on a piece of photosensitive film.
In an internal drum type laser scanner assembly, a piece of film is positioned onto a film platen, wherein the film platen has a partial cylindrical or partial drum shape. The photosensitive film is positioned against the film platen. The laser or optical scanning system is positioned at the center of curvature of the photosensitive film for scanning a scan line across the photosensitive film surface. A linear translation system moves the laser or optical scanning system lengthwise along a longitudinal axis as defined by the center of curvature of the film to expose an entire image onto the film.
The film may be fed into the film platen utilizing a film transport system which often incorporates a plurality of feed rollers. Once the piece of photosensitive film is fed onto the film platen, the film must be held tight against the curved surface of the film platen, and centered and aligned into a scanning position in order for in image to be correctly exposed onto the photosensitive film. Often such methods and mechanisms for aligning and centering a piece of film on the internal surface of the film platen require multiple complex mechanical and electrical components and control systems.